fix: lazy load to prevent instant downloads of wasm on page load

[sqhell]

Changes

• Add clean step to build script (rm -rf dist &&) to prevent old hashed WASM files from accumulating across builds
• Simplify source to single entry point (removed worker helper from entry array) - Parcel now discovers workers through imports, eliminating duplicate
  WASM in single build
• Implement lazy-loading: WASM files (60MB) now download only when user clicks "Connect MetaMask Snap" instead of on page load
• Add yellow "Z" favicon as inline SVG
• Improve error handling for MetaMask connection rejections (code 4001)

Tests

Verify no duplicate accumulation:
cd packages/web-wallet
yarn build
ls -la dist/.wasm # Should show exactly 2 files
yarn build
ls -la dist/.wasm # Should still show exactly 2 files (no accumulation)
du -sh dist/ # Should be ~66MB

Verify lazy-loading:

Open http://localhost:3000 in incognito

DevTools → Network → filter "wasm"

Refresh page → should show 0 WASM files

Click "Connect MetaMask Snap" → now WASM files download

Bandwidth impact:

• Before: 5 WASM files (~178MB) deployed
• After: 2 WASM files (~60MB) deployed
• Casual visitors: 0 WASM bandwidth (lazy-load)

Issues

• Addresses bandwidth spike from 27GB → 174GB/month by eliminating duplicate WASM files
• Reduces new visitor bandwidth cost from ~178MB → ~60MB compressed (~55MB over wire)
• Eliminates WASM download for visitors who don't connect (landing page browsing)